A nuclear reactor of a nuclear power plant is surrounded by a safety vessel formed of concrete and steel, which is referred to as a containment, in which a coolant circulates to maintain a proper temperature. In addition, the nuclear reactor includes an ECCS for cooling the nuclear reactor upon occurrence of failures or accidents.
The ECCS must be operated upon occurrence of accidents such as coolant leakage, etc., to cool the nuclear reactor for 30 days with no external interference. The ECCS is a system for collecting coolant discharged and water sprinkled upon a pipe failure into a sump disposed at the lowermost part in the containment, sprinkling the water from an upper part of the containment using the re-circulation pump to cool the containment, and circulating some of the water through a nuclear reactor cooling system to remove remaining heat of the nuclear reactor using a remaining heat removing pump.
When coolant leakage occurs due to damage to a pipe, etc., in a primary system of the nuclear power plant, foreign substances such as lagging materials, coating materials, latent foreign substances, etc., are generated due to discharge of a coolant. In addition, the discharged coolant and water sprinkled from a sprinkler system of the containment move all foreign substances to a re-circulation sump disposed at a lower end of the containment of the nuclear reactor. Therefore, in order for the foreign substances not to decrease performance of the ECCS, a filtration apparatus is provided in front of an introduction part of a suction pipe guided to an emergency cooling pump.
When a high temperature and high pressure pipe is broken, foreign substances such as fragments of lagging materials, coating materials, etc., are generated and moved toward the sump, and the filtration apparatus functions to filter the foreign substances moved to the sump and supply the filtered water into the re-circulation pump, without interfering with the operation of the re-circulation pump.
The filtration apparatus ensures that the foreign substances generated due to accidents can be filtered and the water can appropriately pass therethrough. In this case, a pressure drop due to the foreign substances must be guaranteed not to exceed an allowable critical value.
A conventional filter screen used in a pressurized water reactor type nuclear power plant has a small screen surface only, and the screen surface is mainly formed of flat grid segments. Thus, when the screen surface is contaminated with fiber settlings, a pressure drop at the screen may be largely increased to an unallowable level.
However, the filtration apparatus having a single surface may be easily deformed by a high pressure, and a small effective filtration area per a unit volume may decrease filtration efficiency. In order to solve the problem, while the number of filtration apparatus may be increased, their installation cost is high, which causes economical problems. Therefore, a filtration apparatus capable of increasing a filtration area per unit volume is still needed.